There are extensive threads detailing things like total dissolved solids, pH levels, flavor, etc. of various kinds of bottled water and the effectiveness of different kinds of filtration and purification systems.

Personally, I find that, for everyday drinking, nothing beats the cost-effectiveness, ease, and taste of filtered tap water using something like a Brita pitcher. For special occasions and teas a nicer bottled water like Iceland Spring can be nice.

Green teas and high roast oolongs are often better with different water though, so there's no one magical water for everything.

Water threads seem to pop up periodically, maybe a few times a year. Sometimes they deal with specific topics. For instance, when I first joined the forums, it was trendy to purify water with bamboo charcoal. More recently, I have seen threads about using tetsubin to improve the mouthfeel and flavor of teawater.

I think we could use a water sticky since the topic comes up so frequently.

Regarding its effect on water, I think it is supposed to slightly purify water and absorb unwanted smells/tastes. I've started using it and would say there's a slight difference in the way my water tastes—in a good way.

As a Norwegian I can attest to that, Voss is a well marketed expensive tap water. A few weeks ago they did a blind test of different waters in a newspaper here, and normal tap water from Oslo actually beat Voss in taste.

Right now I normally just use tap water which is pretty soft, and normally without any chemical taste or smell. When I lived in the UK with very heavy chlorination I normally bought different spring waters for my teas. Some of them worked better than others. I tried to avoid spring water with a very high mineral content. IMHO they don't do your tea any good. I also tried using a brita filter for a while, but I could still taste the chlorine in some teas, especially finer oolongs. If it was a very strong red/black tea it was less noticeable though.

When I looked for bamboo charcoal over a year ago, I could only find it sold in very small amounts (and very expensive). Then Yunnan Sourcing started carrying it (in bulk, too), so if you ever order from them (you can get it here), check it out.